(2025) Energy_The role of carbon dioxide in hydrocarbon conversion during catalytic pyrolysis of plastic mixture over Ni catalyst

Jeong H.; An G.; Lee D.-J.; Kwon E.E.; Jung S.

(Elsevier Ltd) Energy ISSN: 3605442 Vol.335 Issue. Article No.137957 DOI: 10.1016/j.energy.2025.137957

 Pyrolysis converts plastic waste to fuel range hydrocarbons (HCs) and industrial chemicals but requires high purity polyolefin waste. However, practical plastic waste is a heterogeneous mixture, enabling a limited amount of high purity plastic recycling. Pyrolysis of mixed plastic produces low quality plastic oil, necessitating a series of refining processes to obtain low yield of target chemicals. In contrast, catalytic pyrolysis can directly convert mixed plastic into higher value syngas, but rapid catalyst deactivation by carbon deposition is a problem. In this study, a sustainable platform for mixed plastic to syngas was developed by introducing Ni/Al₂O₃ as a catalyst and CO₂ as a feedstock gas. Volatile HCs evolved from pyrolysis of plastic were decomposed over Ni catalyst to produce shorter chained HCs and H₂, but catalyst deactivation was shown by carbon deposition under N₂. When CO₂ was introduced, HCs were further converted into syngas (H₂ and CO) by catalytic reactions with CO₂, suppressing carbon deposition on catalyst. The best yield of gaseous products from catalytic pyrolysis of a polypropylene was 377 % at 650 °C under CO₂, which was more than 7 times higher gas yield under N₂. When heterogeneous plastic mixture was used as a reactant, the same trend was shown, and the presence of aromatic plastics in plastic mixture increased the yield of aromatic compounds. This study experimentally demonstrated that low quality plastic mixture and CO₂ could be simultaneously converted into syngas by catalytic pyrolysis with suppression of carbon deactivation. © 2025 Elsevier Ltd

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government ( MSIT ) (No. RS-2024-00344059 and No. RS-2023-00219667 ).